After quite a gap, I’ve at last got around to writing two further articles, for those interested in usingThe first article explains how to set up Qsynth with Sonic Pi on a Raspberry Pi or linux based computer running Sonic Pi. Unfortunately, for Raspberry Pi you need to install your own version of Sonic Pi built from Source, as the version currently supplied with the latest Raspbian Buster dated 2019-09-26 although built from Sonic Pi 3.1 source, does NOT include essential elements necessary for Midi or OSC communications to work.
I hope to publish details on building version 3.1 for Sonic Pi shortly, together with a bundled download that will let you install it, although not a full blown debian package which is difficult to build.
The first article details how to to install and connect Qsynth to Sonic Pi, tested on a full Sonic Pi 3.1 version running on a Pi4.
The second article details various techniques using OSC messaging to control various aspects of the Sonic Pi, like altering effects, volume, pan settings, samples playing in real time. This uses the TouchOSC application available for IOS or Android phones and tablets to send the control signals. This article applies to Sonic Pi running on Mac or Windows as well.